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HP 41C Video interface test. Howto?
07-17-2020, 08:53 PM
Post: #24
RE: HP 41C Video interface test. Howto?
I don't think the schematics are going to be that much help.

The major components are the video controller, the microcontroller, the video RAM, and the HP-IL controller.

The indication is that the display is all triangles, which sounds like a RAM issue, but I don't see that any of the tests have caused the display to change. If it were simply a bad RAM the display should change to some other garbage.

BTW, what's the difference between the ASCII code for a space and a triangle?

Examining the photo, it can be seen that the RAM is connected to 1LF4 chip, the video controller. I'd change the 1LF4 but there's no harm in changing the RAM chips first because it's easier and cheaper.

As mentioned, there's a 1LF4 available at Sphere and I have one I bought a few years ago while trying to fix a jitter problem that I'm willing to sell.

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RE: HP 41C Video interface test. Howto? - Dave Frederickson - 07-17-2020 08:53 PM

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